Cuvette arrangement

ABSTRACT

A cuvette for receiving a quantity of fluid for photometric absorption measurement has a wedge shaped recess in an interior wall in which a beveled fluid supply conduit opens.

0 Wanted States Patent [1 1 [111 3,869,214

Eglli et all. 1 Mar. 4, 1975 [54] CUVETTE ARRANGEMENT [56] References Cited [75] Inventors: Bruno Egli, Rorschach; Nikiaus UNITED STATES PATENTS Mauser, G both of 3,490,850 1/1970 Mayer 356/246 Switzerland 3,493,306 2/1970 Mayer 356/246 0 Assigneez Labtmmc Zurich, Switzerland 3,681,995 8/1972 Paatzsch 356/-46 X [22] Filed: Apr. 24, 1973 Primary Emminer-R0nald L. Wibert Assistant E,\'aminer-Matthew W, Koren [21] Appl' 354150 Attorney, Agent, or Firm-Andrus. Sceales, Starke &

, Sawall [30] Foreign Application Priority Data Apr. 25, 1972 Germany 2202118 [57] ABSTRACT A cuvette for receiving a quantity of fluid for photo- [52] US. Cl. 356/246, 356/181 metric absorption measurement has a wedge Shaped [5 Clt re e i an interior wall in a beveled Sup- [58] Field of Search 356/246, 208, High/158716; ply Conduit Opens 7 Claims, 4 Drawing; Figures PATENTEDNAR 111915 sumaqrz 25 Fig.3

u n m n 7 up 9 L y Q 2 a w i W m WHU H 1 CUVETTE ARRANGEMENT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cuvette or test cell arrangement for receiving a fluid test sample for photometric analysis.

2. Description of the Prior Art Cuvettes, or test cells, of the vacuum type contain three piping connections. One is a vacuum connection above the fluid level in the cuvette. A second connection is the fluid supply piping of the receptacle containing the fluid to be analyzed. The third connection is a fluid exhaust pipe connected to the cuvette in fluid communication with the bottom of the cuvette. Between the cuvette bottom and the test fluid surface a light source passes a light beam through the fluid.

Because the fluid to be analyzed is often expensive and because of the large volume needed for analysis, it is often diluted. However, this is time consuming and introduces the possibility of error.

It is also known to stop the filling of the cuvette by means of an electric relay. As soon as electrodes in the cuvette are immersed in the fluid, a current circuit is completed which, for example, closes a flap valve, or turns off a vacuum pump. However, the electrodes and associated current in the test fluid creates the danger of electrolysis of the test fluid which can cause the test results to become false.

The electrodes are commonly brought within the euvette in the vacuum connection, to facilitate interchange. However, this often results in a higher than required level of test fluid in the cuvette, with the attendant increased expense. The excessive test fluid will wet the electrodes, vacuum connection, and portions of the cuvette not actually necessary for test purposes. This excessive wetting increases the difficulty of flushing the cuvette to prevent test errors.

In presently available cuvettes, the fluid supply conduit discharges into the upper third of the cuvette in proximity to the vacuum connection. This arrangement also wets portions of the cuvette not actually necessary for the analysis and may cause the fluid to uncontrollably enter the vacuum connection.

SUMMARY OF THE PRESENT INVENTION The purpose of the present invention is to provide a through-flowing cuvette in which the volume of test fluid for analysis of absorption properties is diminished to the greatest extent possible without chemical or optical impairment. By controlled flushing of the test fluid the wetting of the cuvette is minimized.

To achieve these and other objects and advantages, the inventive arrangement includes a wedge shaped recess in the cuvette wall slightly below the surface fluid.

. The fluid supply conduit opens into the recess opposite in cross section and the fluid supply and exhaust conduits circular in cross section.

By locating the opening of the fluid supply conduit in the lower third of the cuvette, the cuvette is filled from below. The upper portions of the cuvette do not become moistened and are not required to be cleaned. The slanting of the recess in the cuvette wall at about permits advantageous controlled flow of the test fluid during filling without splashing. Through the rectilinear forming of the hollow body of the cuvette and the cylindrical form of the conduits inside the hollow body, the manufacture of the cuvette will be simplified. Only a small quantity, for example, approximately 0.6 ml. of test fluid is needed to rinse or flush the moistened inner glass parts. The filling height within the cuvette may be controlled by suitable means, such as a light beam so that the filling of the cuvette is limited to approximately the middle thereof. Through this, the test fluid is not subjected to the influences produced by other height control techniques which have heretofore caused errors in the test results.

Because of the required small volume of the test fluid and other analytical fluids which are often expensive, the analysis process will be inexpensive. The small volume and the rapid filling and emptying of the cuvette lend rapidity to the analysis procedure. The reduction, to a minimum, of the fluid moistening of the parts of the cuvette insures that flushing procedures will remove all residue of previous test fluids and insure the accuracy of the analysis.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an overall view of photometric apparatus including the improved cuvette of the present invention.

FIG. 2 is a top plan view of the cuvette of the present invention showing the various connections thereto.

FIG. 3 is a cross section of the cuvette showing'the fluid supply and fluid exhaust conduits within the euvette.

FIG. 4 is a cross section of the cuvette looking to the right in FIG. 3 and showing the opening of the fluid supply conduit inside the cuvette.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, test tube 1 contains a supply of the fluid to be analyzed. As test tube 1 is raised along piping 19, it strikes sensor 3. The sensor 3 pivots about point 4 and operates switch 5 which energizes pump 6 and filling level control 7. If desired, switch 5 can be manually operated, as by movement of sensor 3.

With the commencement of the operation of pump 6, valve 9 is opened. Valve 9 is coupled to restriction or throttle 10 which slows the vacuum action of pump 6. With valve 9 open, valve 11 is closed. As a result, the fluid 12 to be analyzed is drawn into the cuvette to a height 8 determined by a filling level control. This, preferably, is in the middle of the cuvette. Upon reaching the desired level, the filling control 7 turns off pump 6 and closes valve 9.

After the test, by manipulation of switch 5 or the use of a time switch or bimetallic switch, pump 6 may be reenergized. Valve 9 is closed and valve 11 opened. The fluid will be drawn from cuvette 13 in the direction of arrow 14 and deposited in tank 15. The operation may then be repeated.

The advantage of the foregoing is that practically fully automatic testing operation can be obtained. It will be appreciated that the time switch may be operated during the first filling of the cuvette to flush out possible residue from an earlier analysis. Thereafter, theoperation of the apparatus insures that no measuring errors will arise through mixing of the residue from earlier test samples with subsequent test samples. The cuvette will be automatically emptied, filled, emptied, filled, etc.

Switch 16 may be utilized when fully automatic operation of the test apparatus is not utilized. Switch 16 may be operated by the pivoting of sensor 3 to empty the cuvette and prepare the test apparatus for a new test.

FIGS. 2 through 4 show, in detail, the cuvette of the present invention. The body of cuvette is preferably rectangular or square. To connection 17 is connected vacuum conductor 18. When switch 5 is operated by the manipulation of test tube 1, vacuum pump 6 is energized to place the interior of the cuvette under vacuum. The cuvette will fill with the fluid to be analyzed from piping 19 which is connected to connector 32. Exhaust piping 20 is connected to connector 21 of the cuvette.

From FIG. 3 it will be seen that fluid supply piping 19 and fluid exhaust piping 20 are connected to cylindrical glass conduits 22 and 23 by smooth connectors 24 and 25, respectively. The floor of body 26 is slightly inclined. The end of fluid exhaust conduit 23 opens above the lower portion of the inclined floor. Fluid supply conduit 22 opens into the body of cuvette 13 in a wedge shaped recess in the cuvette wall. The wedge shaped recess may typically subtend an arc of 90 and be located in the lower third of the cuvette body.

The test fluid flows in cuvette 13 in the direction of arrow 28 out of the bevelled mouth of conduit 22 and against slant 29 of recess 27. The fluid falls across slant 29 to the base of cuvette 13 without the creation of sprinkling or turbulence. The absorption measurement utilizes light ray 30 which passes through the test fluid at about the height of the wedge shaped recess 27 and the lower end of fluid supply conduit 22.

FIG. 4 is a view of the wedge forming recess 27 showing the opening 31 of the fluid supply conduit 22. The distance of the juncture of the walls of the recess is approximately mm. from the floor so that the filling height 8 of the cuvette is about 16 mm. This places the height slightly about wedge shaped recess 27 and about in the middle of the cuvette body. As a result, the fluid to be analyzed will not be washing around in the portion of the cuvette through which light beam 30 passes.

With the apparatus of the present invention, the danger of mixing the fluid undergoing analysis with that of the following test is essentially diminished. Through a small amount of test fluid needed for the analysis, the expensive costly agents can be saved. If desired, flushing of the cuvette, preferably with distilled water may be used for cleaning it, so that the measuring solution directly out of a test tube, for example, a centrifuge tube, may be taken.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. A cuvette for receiving a quantity of fluid for photometric absorption analysis, said cuvette being suitable for connection to a vacuum source and to a source of fluid to be analyzed and comprising:

a hollow body having an enclosing wall and floor defining an elongated chamber suitable for receiving a quantity of fluid sufficient to establish a preselected level of fluid within said chamber;

a wedge shaped recess in said enclosing wall of said chamber located below said fluid level, said wedge shaped recess having a pair of diverging faces, one of said faces slanting into said chamber;

a fluid supply conduit connectable to the fluid source and having an opening in the other of said faces for discharging fluid onto said slanting face;

means for passing light through the fluid beneath said fluid level; and

a vacuum source connection opening into said chamber' above said fluid level.

2. The cuvette of claim 1 wherein said wedge shaped recess subtends an angle of substantially and said conduit is bevelled at an angle of substantially 45 and said conduit opening is in the lower portion of the chamber.

3. The cuvette of claim 1 wherein said floor is slanting and said cuvette further includes a fluid exhaust conduit opening on said slanting floor.

4. The cuvette according to claim 3 wherein said body and chamber are rectangular and fluid supply conduit and exhaust conduit are of circular cross section.

5. The cuvette according to claim 3 wherein said fluid exhaust conduit is contained within said enclosing wall and positioned generally perpendicular to said floor, said fluid exhaust conduit opening above said floor.

6. The cuvette according to claim 1 wherein said fluid supply conduit is contained within said enclosing wall.

7. The cuvette according to claim 1 wherein said means for passing light through the fluid is located adjacent the fluid supply conduit opening. 

1. A cuvette for receiving a quantity of fluid for photometric absorption analysis, said cuvette being suitable for connection to a vacuum source and to a source of fluid to be analyzed and comprising: a hollow body having an enclosing wall and floor defining an elongated chamber suitable for receiving a quantity of fluid sufficient to establish a preselected level of fluid within said chamber; a wedge shaped recess in said enclosing wall of said chamber located below said fluid level, said wedge shaped recess having a pair of diverging faces, one of said faces slanting into said chamber; a fluid supply conduit connectable to the fluid source and having an opening in the other of said faces for discharging fluid onto said slanting face; means for passing light through the fluid beneath said fluid level; and a vacuum source connection opening into said chamber above said fluid level.
 2. The cuvette of claim 1 wherein said wedge shaped recess subtends an angle of substantially 90* and said conduit is bevelled at an angle of substantially 45* and said conduit opening is in the lower portion of the chamber.
 3. The cuvette of claim 1 wherein said floor is slanting and said cuvette further includes a fluid exhaust conduit opening on said slanting floor.
 4. The cuvette according to claim 3 wherein said body and chamber are recTangular and fluid supply conduit and exhaust conduit are of circular cross section.
 5. The cuvette according to claim 3 wherein said fluid exhaust conduit is contained within said enclosing wall and positioned generally perpendicular to said floor, said fluid exhaust conduit opening above said floor.
 6. The cuvette according to claim 1 wherein said fluid supply conduit is contained within said enclosing wall.
 7. The cuvette according to claim 1 wherein said means for passing light through the fluid is located adjacent the fluid supply conduit opening. 